1. Field of the Invention
The invention herein relates to a process and apparatus for preventing corrosion, and more particularly microbiologically influenced corrosion, as well as galvanic and water influenced corrosion, of a hydraulic elevator cylinder.
2. Background of the Invention
A hydraulic elevator shaft cylinder is normally constructed of steel and installed underground, thus exposing the cylinder to soil and ground water. As a result, corrosion of various types may occur. Because the cylinder is installed beneath the elevator car frame and platform, and typically beneath the building, any repair or replacement of a corroded cylinder necessarily involves substantial difficulties in gaining access to the cylinder. Leakage of hydraulic fluid from a corroded or defective cylinder may create an environmentally hazardous situation.
While corrosion of various types, including water influenced and galvanic corrosion, are known to occur, of particular concern is microbiologically influenced corrosion caused by bacteria such as sulfate reducing bacteria and acid producing bacteria. This type of corrosion will occur when microbiologically rich ground water comes in contact with the cylinder and occurs substantially more rapidly than many other types of corrosion. Therefore, it is a particularly serious problem.
Examples of corrosion causing sulphate-reducing bacteria are those of the genus Desulfovibrio. Bacteria of the genus Gallionella are examples of acid producing bacteria also known to cause corrosion. Corrosion of simple metal pipes caused by these bacteria has been recognized and documented. However, no one has previously described any method for prevention of corrosion of hydraulic elevator cylinders caused by microorganisms.
A number of methods and devices, such as protective coatings and casings, have been utilized to deal with the problem of corrosion to hydraulic cylinders caused by the effects of salts, sulphur, stray currents and other causes. Typical examples are shown in U.S. Pat. Nos. 4,983,072; 5,076,146 and 5,226,751. However, these methods and devices are subject to failure as a result of damage occurring during transportation or installation or due to ground movement after the installation, when the casing may leak or the coating may become damaged, thus breaking the seal and exposing the cylinder to the underground environment of soil, water and bacteria. Additionally, these methods and devices have not addressed the problem of microbiologically influenced corrosion.
Techniques exist for detection and removal of fluid within a casing, such as sensing for the presence of a fluid by the use of pressure. However, such sensing means are located below ground and under cement so that failure of this system cannot be checked. Furthermore, this system does not prevent the growth of bacteria and the resulting damage to the cylinder and further does not prevent damage to the protective casing, caused by earth movement or other movement of the cylinder.
There is clearly a need for an efficient method and device to prevent corrosion, especially microbiologically influenced corrosion, of a cylinder of a hydraulic elevator and to detect the leakage of water into the casing surrounding the cylinder. Furthermore, there is a need for an efficient method to detect the leakage of hydraulic fluid from a corroded or defective cylinder into the casing surrounding the cylinder.